Call metering circuits in telephone systems



L Nov. 24, 1931. N. E. NILSSON 1,833,536

CALL METERING CIRCUITS IN TELEPHONE SYSTEMS Filed June 18, 1930 Patented Nov. 2 4, 1931 i UNITED STATES PAT];

NT; orrlca NILS EMIL NILSSON, or STOGKHOLM, SWEDEN, ASSIGN-ORSTOYTELEFONAKTIEBOLAGET L. M. narosson, or STOGKHOLM, SWEDEN, A REGISTERED oomrm CALL METERING CIRCUITS IN TELEPHONE SYSTEMS Application filed June 18, 1930, Serial No. 462,105, and in Sweden June 21, 1929.

at the contact 1. The relay SR then starts In certain call metering systems in telephone plants it is preferred to have the call meter permanently connected to one of the line branches of the talking connection, usually the third or test wire. Measures must then be taken to prevent an undesirable actuation of the call meter through other currents passing through said line branch. The

present invention has for its object a circuit arrangement of this kind and consists substantially therein that the call meter is blocked against undesirable currents by a rectifier connected into the circuit of the call meter or another similar equivalent device, which lets through the current only in the one direction. The actuation of the call meter is then eflected simply by a change in the potential of the point where the call meter is connected to the line branch in question, which change of potential causes a flow of current in the desired direction.

The invention will be more closely de-, scribed with reference to the accompanying drawing showing a simplified circuit diagram for call metering in an automatic telephone system. 7

The subscribers line L is provided with a line relay LR, acut ofi relay BR, and a call meter SM which, according to the invention, isconnected to the third wire '0 belonging to the subscribers line over a rectifier LS which may be or" any arbitrary known kind. Preferably a metallic rectifier is used. The two talking line branches A, B of the subscribers line together with the third wire 0 are in the shown example connected to fixed contacts, ale, bk, 0k in the contact field of the'call finder of which only the test contact arm PK and a stop relay PR are shown on the drawing. The line and cut oil relays are provided with two contact springs k is, which are adapted to be actuated by the two relays.

Upon a call, the line relay LR is first energized in the usual manner over a subscribers line, the circuit of the relay SR being closed the call finder in known manner. When said finder finds the calling line a circuit 2 is closed over the third wire through the cut oil relay BR which disconnects the line relay LR and locks itself over the contact 3. At the same time the call finder is brought to stop.

As shown on the drawing, the call meter SM is included between the earthed positive pole of the central battery, not shown on the drawing, and the third wire 0. The rectifier LS is included between the call meter and the third wire in such a manner that said current closing over the third wire has no influence upon the call meter as that current, which otherwise would pass from the positive pole of the central battery to the third wire, is blocked by the rectifier.

The call meter may then, without disturbing the talking connection, be actuated one or more times by changing the potential in the third wire 0 in such a manner that current is passing through the call meter in the direction from the third wire. In the shown example this is brought about by that the third wire, by means of the contact device K, is switched without current interruption from the positive pole of the central battery to the positive pole of an additional battery EB which is series connected with the central battery and thus by its negative pole is connected to earth. A resistance R prevents short-circuit of the battery EB during the shifting. By said shifting a circuit 3 is now closedv through the call meter SM in which circuit the current flows in such a direction that the call meter is actuated. In systems having timing, the call meter may in this manner be actuated during the conversation an arbitrary number of times by a repeated actuation of the contact device K.

I claim:

1. In a telephone system, a line, a call meter connected to one of the line branches, a rectifying device which lets through current in only the one direction connected in series with the call meter to the line branch.

2. In a telephone system, a line, a call meter connected to one of the line branches, a rectifying device which lets through current in only the one direction connected in series with the call meter to the line branch, a uni-directional current-source connected in series with I the call meter, a central current source, and

10 means to connect the call meter to the branching point between said uni-directional current-source device and said een tral source.

- In testimony whereof I afiix my signature.

' NILS EMIL NILS'SON;

ill, I 

